Flowserve CPXS - Manual (Page 15)

CPXS, CPXNS and CPXPS USER INSTRUCTIONS ENGLISH 71569250 07-11
Page 15 of 48 flowserve.com
excessive, cause misalignment, hot bearings, worn
couplings, vibration and the possible failure of the
pump casing, the following points should be strictly
followed:
•
Prevent excessive external pipe load
•
Never draw piping into place by applying force
to pump flange connections
•
Do not mount expansion joints so that their
force, due to internal pressure, acts on the
pump flange
Ensure piping and fittings are
flushed before use.
Ensure piping for hazardous liquids is
arranged to allow pump flushing before removal of
the pump.
4.6.1.1
CPXS and CPXNS only
Take the suction lift into account in the available
NPSH which must be higher than the required
NPSH of the pump.
In order to minimize friction losses and hydraulic
noise in the pipework it is good practice to choose
pipework that is one or two sizes larger than the
pump suction and discharge. Typically main
pipework velocities should not exceed 2 m/s (6
ft/sec) suction and 3 m/s (9 ft/sec) on the
discharge.
4.6.1.2
CPXPS self primer only
The delivery pipework must permit priming air to
escape unhindered from the pump during the
priming cycle, without back pressure and prevent
excessive run-back of liquid on shutdown to
minimise syphoning.
Priming air may be vented in one of the following
ways:
1. The discharge pipework regulating valve, if
fitted, may be partly opened during the priming
cycle to freely vent the air.
2. An automatic air release valve may be fitted to
the discharge pipework, between the pump and
any valves, providing that gases and vapours
given off are environmentally safe and
acceptable for release into the atmosphere.
3. An air bleed pipe may be run from the discharge
pipework, between the pump and any valves,
back to the suction tank or sump. This
arrangement has a disadvantage in that manual/
automatic control will be necessary during
operation to prevent continuous re-circulation of
the pumped liquid.
4.6.2 Suction piping
4.6.2.1
CPXS and CPXNS suction piping
a) The inlet pipe should be one or two sizes larger
than the pump inlet bore and pipe bends
should be as large a radius as possible.
b) On suction lift the piping should be inclined up
towards the pump inlet with eccentric reducers
incorporated to prevent air locks.
c) On positive suction, the inlet piping must have
a constant fall towards the pump.
d) The pipe next to the pump should be the same
diameter as the pump suction and have a
minimum of two pipe diameters of straight section
between the elbow and the pump inlet flange.
Where the NPSH margin is not large, it is
recommended that the pipe straight is 5 to 10
pipe diameter. (See section 10.3, Reference 1.)
Inlet strainers, when used, should have a net 'free
area' of at least three times the inlet pipe area.
e) Fitting isolation and non-return valves will allow
easier maintenance.
f) Never throttle pump on suction side and never
place a valve directly on the pump inlet nozzle.
g) The pump is fitted with silicon carbide bearings
therefore small non-abrasive solids less than
0.3 mm (0.012 in.) in diameter can be handled
providing they constitute no more than 2.5% by
volume of liquid handled.
h) Solids must be non-magnetic, must not have a
tendency to coagulate and must not be fibrous.
They should also be non-abrasive and must
not scale wetted surfaces. For services other
than above you are recommended to contact
Flowserve for advice.
4.6.2.2
CPXPS suction piping
a) The inlet pipe should be as short as possible,
airtight and the smallest volume as practical for
the pump flow rate so as to be able to prime in
quickly. Where inlet pipe volume is large an inlet
ball-foot valve or flap valve will be required.
b) It is recommended that the pump inlet pipe is no
larger than the pump inlet bore or such that the
suction velocity is in the range of 3 to 5 m/sec
(10 to 16 ft/sec). The piping should slope down
towards the pump casing suction flange.
c) Take the suction lift into account in the available
NPSH, which must be higher than the required
NPSH of the pump.
d) Allow a minimum of two pipe diameters of
straight section between the elbow and inlet
flange.
e) Fitting an isolation valve will allow easier
maintenance.